header {
    text-align: center;
}

main {
    width: 100%;
    height: 100%;
    margin-top: 5px;
    display: flex;
    justify-content: center;
    align-items: center;
}

#board {
    width: 560px;
    height: 560px;
    display: flex;
    flex-wrap: wrap;
    border: 1px black solid;
}

.grid {
    width: 20px;
    height: 20px;
    text-align: center;
    box-sizing: border-box;
    /* border: 1px black solid; */
}